Guess who I'm related to?

Abiola of Foreign Dispatches makes a point that can't be made enough:

The "simple fact" he's referring to is of course the coalescent process. What's important about this quote is that most attempts to draw conclusions about one's identity by tracing one's ancestry rapidly become little more than exercises in fantasy the further back in time we look; if person X is "Jewish" because he had a Jewish ancestor who lived some 500 years ago, then pretty much all of Europe, North Africa and the Middle East is "Jewish" by said criterion, rendering it of dubious value.

The same goes for any other ethnic group one wishes to name: there's almost certainly a little bit of Chinese, Arab, Jewish, Hindu, Roman and everything else that's been around long enough in me, you and every average Joe walking down the street. All that really differs is the weighting of the various pieces.